One type of electronic device is a module. A module includes, among other things, one or more dies (also referred to as chips), which may be semiconductor dies or other types of dies. Modules may be analog, digital, or a combination of analog and digital. An example of an analog module is a bridge rectifier. Several bridge rectifier modules are available from Vishay Intertechnology, Inc.
FIG. 1A is a simplified diagram of a typical bridge rectifier circuit. As shown, four rectifier dies are connected to each other by electrically conducting members. A positive DC (+) output terminal is connected to the cathode (N-type contact of die) of two of the rectifiers, while the negative DC (−) output terminal is connected to the anode (P-type contact of die) of two of the rectifiers. The two AC (˜) input terminals are each connected to an anode of one rectifier and the cathode of another rectifier. FIG. 1B is a cross section of a rectifier die that is used in bridge rectifier modules. The rectifier die is a single crystal semiconductor where the anode side is referred to as p-type and the cathode side is referred to as n-type. The surfaces of both sides of the die have thin metal layers that act as electrically conducting contacts. There is also a passivation layer (such as glass or SiO2) that protects the junction. A concern is if a large metal contact is in contact with the passivation later it may cause the passivation layer to crack because of differences in thermal expansion when the module heats up during normal operation.
Module packaging generally includes an exterior housing that protects the dies associated with the module. An example of an exterior housing is an epoxy housing. A number of leads, generally two or more leads, extend from the housing. The leads facilitate electrical interconnection between the electrodes of the dies and electronic components external to the module. The leads are configured to allow the module to be mounted to a substrate using various techniques, such as through-hole-mounting or surface-mounting techniques.
The leads extending from the housing are connected to the electrodes of the dies within the housing using various techniques. A lead frame is a type of packaging that can be used to provide such connection(s). Designing a lead frame that facilitates the efficient and reliable handling, positioning, and attachment of multiple dies is desirable. For example, it often desirable to use automated processes to concurrently load and attach multiple dies onto a lead frame. It is also often desirable to monitor the quality of the attachment (made by soldering, for example) between the lead frame and the electrodes of the dies.
Some existing lead frame designs reduce the throughput and/or increase the cost of producing modules, especially when automated loading and attachment processes are used. Generally, bridge rectifier modules are constructed with either two similar lead frames or a single lead frame with separate metal jumpers between the dies and portions of the lead frame. For example, one lead frame design requires electrodes of dies to be oriented in different directions. In general, only similarly oriented dies are concurrently loadable using automation—when the dies are differently oriented, automated loading efficiency is reduced. Manual loading is generally less efficient than automated loading. In addition, when dies are oriented in different directions, disparate stresses on die passivation may occur. This is sometimes referred to as the “sandwich effect”. The sandwich effect may cause quality or reliability problems.
Another type of lead frame is composed of more than one piece or more than one lead frame. For example, die pad structures may be designed having two or more pieces, and/or separate jumper structures may be used to connect the electrodes of the dies to the leads. In one example, when four rectifier dies are placed between two lead frames, two of the dies have the p-type (anode) contact facing upwards and the other two dies have the n-type (cathode) contact facing upwards. In another example, all four dies have their anodes facing upwards. The anode of each die is connected with a small metal jumper to the appropriate portion of the lead frame. Since the metal jumpers are small, they are difficult to handle for automated soldering equipment. Also, these jumpers may shift during the soldering process and contact the passivation layers of the dies, resulting in reliability problems. Also, additional solder joints are used between each jumper and the lead frame, which may adversely affect the power-handling capability of the device, because solder has a higher thermal resistance than copper. When lead frames have more than one piece, the likelihood of part positioning errors (and subsequent reliability problems) is increased. Part positioning errors can lead to reliability and production problems, including soldering problems, which result in increased costs and reduced throughput. Having die surfaces hidden from view may make inspection difficult.
It will be appreciated that the claimed subject matter is not limited to implementations that solve any or all of the disadvantages of specific lead frames or aspects thereof.